1. Field of the Invention
The present invention relates to a method for separating an encoder shaft of an angle encoder from a drive shaft, which are axially aligned with each other and are self-lockingly braced on each other by an axial press fit and a central fastening screw, which connects the shaft of the angle encoder and the drive shaft in the axial direction. The present invention further relates to a device for separating this shaft of an angle encoder and this drive shaft.
2. Description of the Related Art
Angle encoders are used as measuring devices for the controllers of electrical drive mechanisms and make measured values available to a position and rpm regulator, as well as for electronic commutation. They are either installed on the housing of the electrical drive mechanism or installed in the drive mechanism housing. FIG. 1 shows an angle encoder 2 installed on the housing of an electrical drive mechanism 1 and containing an encoder shaft which is rigidly connected with the drive shaft of the electrical drive mechanism 1. The self-locking connection of the two shafts, which are axially aligned with respect to each other, is provided by a press fit which is produced by an inner or outer cone of the encoder shaft and a corresponding outer or inner cone of the drive shaft, or by a cylindrical and hollow-cylindrical form fit of both shafts, and a central fastening screw, which connects both shafts with each other in the axial direction. The self-locking bracing of both shafts is accomplished by tightening the fastening screw, whose shank has been passed through a central bore in the encoder shaft, whose screw thread is screwed into an internal screw thread of the drive shaft, and whose screw head rests against the front or bottom of a bore in the front of the encoder shaft.
FIG. 2 shows a longitudinal view through an angle encoder 2, which has been inserted in an installation space of a drive housing 10 of the drive mechanism 1 and into which a drive shaft 4 projects, which is supported by a drive bearing 11 on the drive housing 10. The angle encoder 2 has an angle encoder housing 20, in which a stationary element is arranged, on which a scanning unit 23, 24 for scanning a graduation or code disk 22 and an encoder shaft 3, which is rotatably seated in the stationary element and supports the graduation or code disk 22, are fastened, and which is seated on the stationary element by means of an encoder bearing 21. The angle encoder 2 is coupled by its stationary element to the drive housing 10 in a torsion-proof manner, wherein the torsion-proof coupling can be provided in accordance with EP 0 762 082 A, for example by a stator coupling 15 by radial clamping at the inner circumference, or in the installation space of the drive housing 10.
The drive shaft 4 has an inner cone 40, into which the outer cone 30 of the encoder shaft 3 is pushed. The encoder shaft 3 contains a central, axially directed bore 31, through which a fastening screw shank 51 of a fastening screw 5 has been pushed, whose fastening screw head 50 rests against the front face, or a recess 32 in the front face, of the encoder shaft 3. A fastening screw thread 52 engages an internal screw thread 42 of a blind bore 41 of the drive shaft 4, which is aligned with the central, axially directed bore 31 of the encoder shaft 3.
The outer cone 30 of the encoder shaft 3 is pulled into the inner cone 40 of the drive shaft 4 by tightening the fastening screw 5, and a self-locking press fit between the encoder shaft 3 and the drive shaft 4 is produced in this way.
Accordingly, when removing the angle encoder 2 from the electrical drive mechanism 1 it is necessary after the fastening screw 5 has been removed to pull the encoder shaft 3 and the drive shaft 4, which are self-lockingly braced on each other, apart from each other, or to push them apart, with a considerable force application. In accordance with the prior art, the pushing apart of the encoder shaft 3 and the drive shaft 4, which are braced on each other, is performed with different push-off methods and push-off devices, two of which are represented in FIGS. 3 and 4 and will be briefly explained in what follows.
For pushing the encoder shaft 3 off the drive shaft 4, with which it is self-lockingly connected, the central fastening screw 5 is turned out of the internal screw thread 42 of the drive shaft 5 by a hexagon screwdriver. Thereafter, in accordance with FIG. 3 a setscrew 62 is screwed into the internal screw thread 42 of the drive shaft 4 by a hexagon screwdriver of lesser jaw size, so that the internal screw thread 42 of the drive shaft 4 is not damaged during the subsequent push-off process. Subsequently a special push-off screw 61 is screwed into an internal push-off screw thread 33 of the encoder shaft 3, which is arranged in the central bore 31 in the area of the outer cone 30 of the encoder shaft 3, until the end of the push-off screw 61 comes into contact with the setscrew 52 and the encoder shaft 3 and the drive shaft 4 are axially pushed apart by this, so that therefore the self-locking press fit between the drive shaft 4 and the encoder shaft 3 is cancelled.
Accordingly, with this push-off method two additional screws, namely the setscrew 62 and the push-off screw 61, as well as two different tools for the screws 61, 62 of different head size, are required for separating the encoder shaft 3 from the drive shaft 4, and therefore the angle encoder 2 from the drive mechanism 1.
FIG. 4 shows a further known push-off device, or push-off method, wherein a special push-off screw 63 is supported in the blind bore 41 of the drive shaft 4, which has the internal screw thread 42, and with its external screw thread 64 engages the push-off screw thread 33 of the encoder shaft 3, so that by screwing in the special push-off screw 63, the self-locking press fit between the outer and inner cones 30, 40 of the drive and encoder shafts 3, 4 is cancelled and thereby the angle encoder 2 can be removed from the electrical drive mechanism, for example for maintenance or inspection purposes.
With this push-off method the parts necessary for pushing the encoder shaft 3 off the drive shaft 4 are reduced to the special push-off screw 63 and an additional tool.
However, it is disadvantageous that a special screw is required as the push-off screw 63, which possibly must be adapted to different depths of blind bore 41, depending on the type of the drive shaft 4. Moreover, the diameter of the special push-off screw 63 is relatively narrow and the special push-off screw 63 must be embodied to be relatively long, so that it becomes unstable.
Possibly different depths of the blind bore 41 in different drive shafts 4, which depend on the drive mechanism 1, are also problematical, which makes respectively special push-off screws 63 necessary. This push-off method cannot be employed in connection with a continuous internal screw thread of drive shafts.
A method and a device for pushing an encoder shaft of an angle encoder off a drive shaft, which are connected with each other by a conical press fit, is known from JP 1-270753 A. For pushing the encoder shaft off the drive shaft, a push-off screw thread is arranged in the housing of the angle encoder, which presses directly on the end of the drive shaft. Accordingly, the force required for push-off also acts on the angle encoder housing which, in case of an appropriately solid connection between the angle encoder shaft and the drive shaft, and therefore of the force required to separate the two shafts, can be deformed or destroyed.